BAGHDAD, Iraq — This week’s intense clashes between the Iraqi army and a Shiite militia are part of a strategy to whittle away the power of a radical cleric. But the high-risk gambit could trigger more fighting across the Shiite south — at a time when the cleric’s stronghold in the capital is virtually off-limits.

Prime Minister Nouri al-Maliki has promised to disband militias, including the Mahdi Army of anti-U.S. cleric Muqtada al-Sadr, as a way to curb the sectarian violence propelling Iraq to the brink of civil war. The United States has made clear it views that effort as crucial.

But a full-scale assault by either American or Iraqi forces on al-Sadr’s stronghold of Sadr City is highly risky. Al-Maliki, a fellow Shiite with political ties to the cleric, has publicly criticized a U.S.-Iraqi raid this month on the teeming district in Baghdad, where al-Sadr’s followers maintain control and mete out Islamic justice in religious courts.

With Sadr City thus out of play for the time being, the U.S. military and its partners have been going after al-Sadr’s forces outside the capital, arresting a Mahdi commander in Basra and raiding militia offices in other cities to cut into the cleric’s power base.

The fighting Sunday and Monday in Diwaniyah, a ramshackle Shiite market town about 100 miles south of Baghdad, was the latest and one of the most intense examples.

The trouble started when Iraqi soldiers arrested one of the cleric’s supporters before dawn Sunday, said an al-Sadr aide. Later in the day, Iraqi soldiers launched more raids and fighting broke out.

Al-Maliki’s office said 73 people, including 23 Iraqi soldiers, were killed before a truce was reached on Monday. Other officials put the death toll at 40, most of them soldiers and civilians caught in the crossfire.

“The battle may be over, but the campaign to clean that city up and to restore it to Iraqi government control isn’t finished,” the top U.S. commander, Gen. George W. Casey, told reporters Wednesday.

A test of loyalty
Such confrontations test the loyalty of Iraq’s mostly Shiite army and police, whose ranks have been infiltrated by al-Sadr’s supporters.

But military moves are all the more risky because of the intense rivalry within various Shiite parties and militias — all competing for power. Diwaniyah, for example, is controlled by a rival Shiite party, leading al-Sadr aides to blame local officials from the other party of essentially using the national army to deal with their rivals.

The fighting in Diwaniyah thus points to one of the most serious problems facing Iraq — the possibility that trouble will spread widely throughout the quieter, calmer south.

With its overwhelmingly Shiite population, most of the south has been spared the Sunni-Shiite fighting that has rocked Baghdad. But the internal Shiite divisions pose a threat.

Another raid earlier this month on the office of a relatively obscure cleric, Mahmoud al-Hassani, triggered a day of street fighting in the Shiite city of Karbala and protests in Nasiriyah and Basra.

Popular maverick
Within the Shiite community, al-Sadr is clearly a dominant figure. His popularity among impoverished Shiites has eclipsed those of mainstream Shiite politicians. Even the country’s top Shiite cleric, Grand Ayatollah Ali al-Sistani, has been loathe to speak out publicly against al-Sadr.

Yet since the beginning of the U.S. mission in 2003, American officials have struggled to find a way to deal with him.

In 2004, U.S. authorities issued an arrest warrant accusing him of a role in the murder of a moderate cleric. That triggered two armed uprisings that ended when the Americans bowed to Shiite pressure and spared al-Sadr and shelved the arrest warrant.

Since then, al-Sadr has become a player. His movement controls 30 of the 275 seats in the national parliament and five Cabinet ministries, and his support was critical to al-Maliki winning the post of prime minister.

Name unmentionable for U.S. forces
Now, the U.S. military rarely mentions his name or his militia’s in connection with sectarian violence, even though U.S. officials say privately that the Mahdi Army is behind much of it. And Iraqi officials invariably speak of incidents involving “breakaway elements,” enabling al-Sadr to disavow responsibility for his followers’ actions.

Al-Sadr has described the Diwaniyah fighting as “individual acts that occurred without instructions” from him, according to one of his spokesmen, Sheik Mohammed Jamil.

In fact, it is unclear how much control al-Sadr does wield over the Mahdi militia, which appears to lack a cohesive command structure, and al-Sadr aides have complained about renegades.

Equally unclear are al-Sadr’s ties to Shiite-dominated Iran. U.S. Ambassador Zalmay Khalilzad contends Iran has urged Shiite militias to fire mortars and rockets on the Green Zone and says splinter groups of the Mahdi Army are behind the attacks.

Others doubt al-Sadr, whose politics are strongly nationalistic, is beholden to the Iranians, who instead have directed most of their aid to mainstream Shiite parties. A recent study by the International Crisis Group think tank concluded that al-Sadr receives “at best, limited material support from Iran.”

“Learning the hard way, the U.S. and its allies have had to recognize the reality of the Sadrists’ strength,” the group wrote.